The present invention relates to capsules for and a method for encapsulating radioactive materials used for medical treatments.
Various methods for utilizing radioactive materials in radiation therapy are known. Of these, a well known method for administering the radioactive source is by the use of small radioactive "seeds". Such seeds comprise a radioactive source contained within a sealed capsule. The seeds are injected or implanted into the patient's body tissue at the site being treated.
Because these seeds are implanted in the human body, the capsule for containing these materials must be securely sealed. Otherwise, undesired leakage from the capsule may occur. The U.S. Food and Drug Administration and the U.S. Nuclear Regulatory Commission have strict requirements for encapsulation of the radioactive material to prevent leakage and resultant injury to patients and medical personnel handling such materials.
In the past the most advantageous materials for encapsulating radioactive materials included stainless steel, titanium and other low atomic number metals. However, there still exist problems of adequately sealing capsules made from these materials. Such metallic capsules are typically sealed by welding. However, welding of such small capsules is difficult. Welding such small capsules may locally increase the capsule wall thickness, or introduce higher atomic number materials at the end or ends of the capsule where the welds are located, and the presence of such localized anomalies may significantly alter the geometrical configuration at the welded end or ends, resulting in undesired shadow effects in the radiation pattern emanating from the source. Other methods of forming the capsules include drilling a capsule form in a metallic block and plugging to form a seal. However, this method suffers from the disadvantage that a capsule having uniform wall thickness is difficult to obtain, and the resulting source will not be able to uniformly distribute radiation.
Lawrence U.S. Pat. No. 3,351,049 discloses a metallic container for containing a radioactive isotope wherein the metallic container is closed and sealed by intermetallically joining the walls under pressure or by ultrasonic welding. Other techniques for welding the structure, depending on the material utilized, are also disclosed. Kubiatowicz U.S. Pat. No. 4,323,055 discloses similar methods for encapsulating radioactive material. Methods for sealing the titanium container of Kubiatowicz include laser, electron beam or tungsten inert gas welding. Kahn U.S. Pat. No. 2,269,458 discloses a somewhat primitive form of encapsulation of radioactive substances wherein the capsule is formed by screwing two threaded parts together.
All of the foregoing methods of encapsulating radioactive materials have substantial shortcomings in providing a capsule which is easy to construct while providing adequate protection against leakage, while permitting uniform radiation therethrough.